Let's start by looking at some concurrency bugs. Here is a simple example of incrementing a counter:
public class Counter { private int counter; public int incrementAndGet() { ++counter; return counter;}
This code is not thread-safe. If two threads are running using the same object concurrently, the sequence of counter values each gets is essentially unpredictable. The reason for this is the ++counter operation. This simple-looking statement is actually made up of three distinct operations, namely read the new value, modify the new value, and store the new value:
As shown in the preceding diagram, the thread executions ...
